The inherited physical and chemical stability of the insulin molecule is a basic condition for insulin therapy of diabetes mellitus. These basic properties are fundamental for insulin formulation and for applicable insulin administration methods, as well as for shelf-life and storage conditions of pharmaceutical preparations. Use of solutions in administration of insulin exposes the molecule to a combination of factors, e.g., elevated temperature, variable air-liquid-solid interphases as well as shear forces, which may result in irreversible conformation changes, e.g., fibrillation.
Unfortunately, many diabetics are unwilling to undertake intensive therapy due to the discomfort associated with the many injections required to maintain close control of glucose levels. This type of therapy can be both psychologically and physically painful. Upon oral administration, insulin is rapidly degraded in the gastro intestinal tract and is not absorbed into the blood stream. Therefore, many investigators have studied alternate routes for administering insulin, such as oral, rectal, transdermal, and nasal routes. Thus far, however, these routes of administration have not resulted in effective insulin absorption.
Efficient pulmonary delivery of a protein is dependent on the ability to deliver the protein to the deep lung alveolar epithelium. Proteins that are deposited in the upper airway epithelium are not absorbed to a significant extent. This is due to the overlying mucus which is approximately 30-40 μm thick and acts as a barrier to absorption. In addition, proteins deposited on this epithelium are cleared by mucociliary transport up the airways and then eliminated via the gastrointestinal tract. This mechanism also contributes substantially to the low absorption of some protein particles. The extent to which proteins are not absorbed and instead eliminated by these routes depends on their solubility, their size, as well as other less understood characteristics.
It is, however, well recognised that the properties of peptides can be enhanced by grafting organic chain-like molecules onto them. Such grafting can improve pharmaceutical properties such as half life in serum, stability against proteolytical degradation and reduced immunogenicity.
The organic chain-like molecules often used to enhance properties are polyethylene glycol-based chains, i.e., chains that are based on the repeating unit —CH2CH2O—. Hereinafter, the abbreviation “PEG” is used for polyethyleneglycol.
Classical PEG technology takes advantage of providing polypeptides with increased size (Stoke radius) by attaching a soluble organic molecule to the polypeptide (Kochendoerfer, G., et al., Science (299) 884 et seq., 2003). This technology leads to reduced clearance in man and animals of a hormone polypeptide compared to the native polypeptide. However, this technique is often hampered by reduced potency of the hormone polypeptides subjected to this technique (Hinds, K., et al., Bioconjugate Chem. (11), 195-201, 2000).
Insulin compositions for pulmonary administration comprising a conjugate of two-chain insulin covalently coupled to one or more molecules of non-naturally hydrophilic polymers including polyalkylene glycols and methods for their preparation are disclosed in WO 02/094200 and WO 03/022996.